1. Field of the Invention
The present invention relates to a voltage regulating apparatus, and more particularly, to a voltage regulating apparatus capable of reducing current consumption and reducing an amount of time used until stably operating when regulating a supply voltage provided from a power supply into a voltage required for operating a semiconductor device.
2. Description of the Related Art
In general, semiconductor devices operate by receiving a driving voltage provided by an external power supply. Since a size of the voltage provided from the power supply is fixed, to drive semiconductor devices operating by a voltage with a different size from the output voltage of the power supply, a voltage regulating apparatus for generating a voltage with a size capable of driving a corresponding semiconductor device by regulating the voltage outputted from the power supply is required.
FIG. 1 is a circuit diagram illustrating a conventional voltage regulating apparatus.
Referring to FIG. 1, the conventional voltage regulating apparatus includes a voltage comparator 11, a current sink unit 12, and a voltage output unit 13. The voltage comparator 11 includes a plurality of metal-oxide-semiconductor field-effect transistors (MOSFETs) 111 to 114 with a circuit structure of a differential amplifier and compares a reference voltage Vref inputted outside with an output voltage of the voltage regulating apparatus. The current sink unit 12 may be embodied as an MOSFET and provides a sink current to the voltage comparator 11. Also, the voltage output unit 13 includes an MOSFET 131 operating according to a voltage comparison result and resistors R1 and R2.
The voltage regulating apparatus applies the reference voltage Vref to a gate of the MOSFET 111 and applies the output voltage to a gate of the MOSFET 114 to compare sizes of the reference voltage Vref and applies the output voltage. When the applied output voltage is smaller than the reference voltage Vref, a voltage across a drain of the MOSFET 111 becomes “low”. Since the voltage across the drain of the MOSFET 111 is applied to a gate of the MOSFET 131 of the voltage output unit 13, the MOSFET 131 is turned “on”. Accordingly, the output voltage is increased. On the other hand, when the output voltage is smaller than the reference voltage Vref, the output voltage is decreased by similar operations. As the increase and decrease of the output voltage are repeated, a voltage across the gate of the MOSFET 114 is regulated to be a size identical with the reference voltage Vref.
In the conventional voltage regulating apparatus, a band-gap voltage generated by a band-gap circuit is generally used as the reference voltage Vref. There is a problem of a large current consumption in the band-gap circuit itself. Also, since the conventional voltage regulating apparatus provides the sink current via one MOSFET 121, there is a problem of a very long settling time for regulating the output voltage to be identical with the reference voltage Vref in an apparatus requiring a small current consumption.
Accordingly, a voltage regulating apparatus capable of reducing current consumption as well as reducing a settling time has been required.